Estimation of measurement uncertainty of a system of bearing diagnostics based on instantaneous power analysis

: W artykule przedstawiono sposób szacowania niepewności układu pomiarowego, składającego się z dzielnika napięcia oraz bocznika, który wykorzystano do badań diagnostycznych łożysk silników indukcyjnych. Wyniki analizy metrologicznej pozwalają sprecyzować, jakiej niepewności pomiarowej można się spodziewać, dokonując badań diagnostycznych łożysk silników indukcyjnych w określonych warunkach, na stanowisku badawczym metodą pomiaru i analizy mocy chwilowej.Because of the fact that the majority of failures in electric motors is caused by bearing damage, a particularly dynamic development in this area of diagnostics can be observed [1, 2, 3, 4]. Bearing diagnosis is possible by measurement and analysis of the values of engine power supply. The diagnostics is possible as bearing damages generate an additional component in the motor current spectrum [5, 6, 7, 8]. Furthermore, the waveform of power supply instantaneous values is deformed [1, 3]. This way, one of possible diagnostic symptoms is the instantaneous power consumed by a motor. A measuring system for investigations of instantaneous power is presented in this paper. Fig. 1 shows a block diagram of the system. The paper describes a metrological analysis of the bearing diagnostic system designed for measuring the instantaneous power. Because measurements of current and voltage are commonly made, to solve various measurement problems, the author decided to develop a methodology for estimating the measurement system uncertainty. Fig. 2 presents the approach for determination of the measurement uncertainty. For the system with a shunt and a voltage divider for current and voltage measurements the uncertainty of type B was estimated with the assumed rectangular distribution of the resistor error limit [1, 3]. The extended uncertainty Up of the instantaneous power measurement was also assessed. This uncertainty was determined at the assumed confidence level equal to 95% and the extension coefficient k = 2 [1, 2, 11]. The uncertainty for the voltage value of 230 V and the current value of 2,9 A is equal to Up = 0,28 VA. Thus, the uncertainty of the instantaneous power measurement in this system exceeds 0,1% of the value of the measured instantaneous power slightly